1. Field of the Invention
This invention relates to a catalyst composition and its use in catalytic cracking processes. More particularly, the invention is concerned with a fluid cracking catalyst which has improved activity and selectivity for producing high octane gasoline fractions from petroleum gas oil feedstocks.
2. Description of the Prior Art
As is well known, the catalytic cracking of heavy petroleum fractions is one of the major refining operations employed in the conversion of crude petroleum oils to desirable fuel products such as heating oils and high octane gasoline. Illustrative of "fluid" catalytic conversion processes is the fluid catalytic cracking process wherein suitably preheated high molecular weight hydrocarbon liquids and vapors are contacted with hot, finely-divided, solid catalyst particles, either in a fluidized bed reactor or in an elongated riser reactor, and maintained at an elevated temperature in a fluidized or dispersed state for a period of time sufficient to effect the desired degree of cracking to lower molecular weight hydrocarbons suitable as gasoline fractions.
A wide variety of petroleum cracking catalysts are described in the literature and are commercially available for use in fluidized cracking processes. Commercial cracking catalysts currently in use generally comprise a crystalline aluminosilicate zeolite cracking component in combination with an inorganic oxide matrix component. Typical zeolites combined with the inorganic oxide matrix include hydrogen- and/or rare earth metal-exchanged synthetic faujasite of the X or Y-type. The matrix materials generally include amorphous silica-alumina gel and/or a clay material such as, for example, kaolin.
Cracking catalysts which are commercially used for the production of gasoline must exhibit good activity and selectivity. The activity of a catalyst is generally referred to as the ability of the catalyst to convert heavy petroleum fractions to lower molecular weight fractions. Under a given set of operating conditions, the degree to which the catalyst converts the feed to lower molecular weight materials is a measure of the catalyst activity. Thus two or more catalysts can have their activities compared by the level of cracked products made by each catalyst under the same process conditions. The selectivity of a catalyst refers to the fraction of the cracked products in a particular boiling or molecular weight range; e.g., C.sub.5 /430.degree. F. naphtha, C.sub.3.sup.- dry gas, carbon, etc. A more special measure of selectivity is the octane rating of the C.sub.5 /430.degree. F. naphtha hereafter referred to as octane producibility. Hence it is most desirable for a preferred cracking catalyst to exhibit both high cracking activity, a high selectivity to gasoline (C.sub.5 /430.degree. F.) boiling range material, and of high octane number producibility, that is the ability to produce gasoline boiling range material with a high octane rating. Unfortunately, catalysts having the highest activity do not produce the highest octane naphtha products and vice versa. As an example, the amorphous silica-alumina cracking catalyst used prior to the advent of the present day zeolite cracking catalyst is less active than the present day zeolite cracking catalysts for cracking the gas oil feedstock, is less selective in the yield of C.sub.5 /430.degree. F. naphtha, but produces a higher octane number naphtha than conventional zeolite cracking catalysts.
The individual components of the catalyst composition of this invention are described in the literature. The specific combination of the components of the invention to produce a highly active and selective catalyst for the production of high octane gasoline is not believed to be shown in the prior art. For example, U.S. Pat. No. 3,312,615 describes a three component catalyst system comprising a crystalline aluminosilicate, substantially inert fines and an inorganic oxide matrix therefor. The crystalline aluminosilicate includes a wide variety of zeolites such as zeolites X, Y, A, L, D, R, S, T, Z, E, F, Q, B, ZK-4, ZK-5 as well as naturally occurring zeolites including chabazite, faujasite, mordenite, and the like. The substantially inert fines include alpha-alumina, barytes, zircon, zirconia, kyanite, and rutile fines.
U.S. Pat. No. 3,542,670 describes a cracking catalyst made by combining a silica-alumina hydrogel with a boehmite amorphous hydrous alumina, and a crystalline alumino-silicate having pores in the 8-15 A range and a silica-to-alumina mol ratio greater than 3:1. The crystalline alumino-silicate includes a variety of zeolites which are exchanged with various ions including hydrogen, and nonpoisoning metals such as rare earth metals.
U.S. Pat. No. 3,816,342 is directed to a process for preparing a fluid catalytic cracking catalyst containing a highly active crystalline aluminosilicate and a relatively less active matrix material. The patentee claims the crystalline aluminosilicate materials having the general formula: EQU M.sub.2 /.sub.n O Al.sub.2 O.sub.3 YSiO.sub.2 .multidot.ZH.sub.2 O
in the salt form, wherein n is the valence of the metal cation M, Y is the number of moles of silica, and ZH.sub.2 O is the water of hydration. Zeolites Y and X are described as being among the most suitable synthetic crystalline alumino-silicates. The matrix materials are described as inorganic oxide gels, such as those of silica-zirconia, alumina, magnesia, and combinations thereof with one another, clays, alumina, metals and refractory materials.
U.S. Pat. No. 3,930,987 describes a cracking catalyst comprising a composite of crystalline aluminosilicates containing rare earth metal cations dispersed in an inorganic oxide matrix wherein at least 50 wt. % of the inorganic oxide is silica and/or alumina. The matrix preferably is made up of silica-alumina, silica-zirconia or silica-zirconia alumina, desirably along with a weighting agent preferably clay and/or alumina. Alpha alumina is preferred in the event alumina is employed.
U.S. Pat. No. 3,717,587 describes the preparation of a cracking catalyst composition containing a wide variety of crystalline aluminosilicates dispersed in an inorganic oxide gel matrix containing a weighting agent. The patent specifies that the most preferred weighting agent is kaolin clay. Other suitable weighting agents include zirconia, alpha alumina, mullite, alumina monohydrate, alumina trihydrate, halloysite, sand, metals such as aluminum and titanium, etc.
U.S. Pat. No. 3,788,977 relates to a cracking catalyst for increasing the amount of aromatic gasoline fractions from gas oil feedstocks. The cracking catalyst is described as a composition comprising a number of zeolite components in combination with minor amounts of a reforming-like additive which consists of uranium oxide and/or platinum metal impregnated upon an inorganic oxide support. The zeolites contemplated by patentee include hydrogen and/or rare earth metal exchanged synthetic faujasites which have silica to alumina ratios on the order of 2.5 up to about 6, including type X or Y faujasites. In addition to rare earth metal exchanged faujasites, patentee contemplates the use of low soda content zeolites.